With 53 American vagrant species involving 214 individuals seen, the birding season of 2023 on Corvo, Azores, was the best year on record since the island's birding potential was discovered in 2005. The previous record year was 2017 with 48 species of 155 individuals – in some of the quietest years there have only been 19 (2006) and 24 (2014) American vagrant species.
Following a few relatively quiet years, partly attributed to restrictions from the coronavirus pandemic and a reduction in low-latitude Atlantic storms, 2023 witnessed not just a return to form but a surpassing of all expectations. Highlights included the Western Palearctic's (WP) first Mourning Warbler, fifth Wilson's Warbler and Eastern Wood Pewee, sixth Wood Thrush, sixth and seventh White-eyed Vireos, seventh Bay-breasted and Chestnut-sided Warblers, eighth Yellow-throated Vireo, ninth Blackburnian Warbler, 10th Grey Catbird (only the second record for the Azores and first for Corvo of this much-anticipated species), 12th Tree Swallow and 13th Yellow-crowned Night Heron.
In addition, two records of apparently newly arrived moorhens (one found dead on the airfield and one in a hedge) showed circumstantial and plumage/structural features that suggested they might have a Nearctic origin. Common Gallinule, a recent split from Common Moorhen, would be a first for the WP. The dead specimen has been retained with the Corvo Biosphere Park Ranger and samples have been sent to Martin Collinson's lab for DNA analysis.
| Category | Species count | Individual count |
| American landbirds | 36 | 181 |
| American waterbirds | 17 (18) | 33 (35) |
| Total American vagrant species | 53 (54) | 214 (216) |
Above: table of American vagrants on Corvo, Azores, in autumn 2023 (species/individuals pending confirmation listed in brackets). For a more detailed breakdown, see Appendix 1.
Furthermore, there were record tallies for certain species including an incredible 17 Swainson's Thrushes, 18 Black-and-white Warblers, 11 Ovenbirds, Common Yellowthroats and Rose-breasted Grosbeaks and nine Grey-cheeked Thrushes.
Mourning Warbler at Lighthouse Valley, Corvo. The first for the Western Palearctic. Identification features include the broken eyering (broken on the anterior and posterior edges of the eye) and the relatively bright yellow underparts and short wing projection compared to Connecticut Warbler. Also, the vocalisations are subtly different (Vincent Legrand).
Early days
The 2023 season began early when Tim Collins arrived on 11 September, but things were relatively quiet with a couple of Lesser Yellowlegs and a Hudsonian Whimbrel in the caldera being the only American birds present. Over the next few days a few new waders arrived, including Semipalmated Plovers and Semipalmated Sandpipers. On 15 September, the first American passerine for the year was reported – an American Yellow Warbler, which unfortunately was not photographed. By 16th a few more birders had arrived, as did a Buff-breasted Sandpiper, but it remained quiet for a couple of days after, with a Greenshank arriving from the 'wrong' direction.
Things started to pick up on 20 September as Hurricane Lee moved around the Atlantic, with a Black-and-white Warbler in the Tennessee Valley and a Red-eyed Vireo in the village, both found by Tim. There were also new Pectoral Sandpipers and White-rumped Sandpipers. Meanwhile, back in the UK, the same weather had reached Pembrokeshire and things had 'gone ape' there as one of the best American bird landfalls on record for the UK began to unfold.
Male American Yellow Warbler, Lower Fields, Corvo (David Monticelli).
Late September mayhem
On 21 September, things escalated when Tim found the second Blackburnian Warbler for the Azores. The next day, reinforcements reached the island when Peter Stronach and Bob Swann arrived amid the incoming weather systems (see Appendix 2) which they had anticipated and thus scrambled from the Scottish Highlands to Corvo. The situation escalated faster by 22nd with a new Black-and-white Warbler and a Chestnut-sided Warbler joining the Blackburnian Warbler at Fojo and, by 23rd, things had got decisively barmy with two new Black-and-white Warblers, two Ovenbirds, a flock of five American Cliff Swallows and at least five new Red-eyed Vireos joining the now-accumulating list of vagrants now on the island.
On 24th, a Baltimore Oriole, three Common Yellowthroats, an American Redstart, a Northern Parula and a Tennessee Warbler were discovered. Surely things could not improve further? But, on 25th, Pierre-André Crochet, Peter Stronach and Bob Swann discovered an Oporornis warbler at the Lighthouse Valley that on initial impressions and consultation with US experts pointed towards the second Connecticut Warbler for the WP.
Over the next few days in challenging weather conditions the bird was occasionally seen and sound recorded, and eventually on 28th Vincent Legrand managed definitive photographs that, with the assistance of US birder Alexis James, allowed the identity of the bird to be confirmed as the first Mourning Warbler for the WP. Also, on 25th, Corvo regular Olof Jonsson had arrived and found new American Yellow and Black-and-white Warblers (there were four of the latter that day), while new Philadelphia Vireo and Northern Harrier were also seen.
Mourning Warbler, Lighthouse Valley, Corvo (Vincent Legrand).
Olof struck again on 26 September with a Wilson's Warbler and a Grey-cheeked Thrush, while Pete and Bob found a new American Yellow Warbler and another Black-and-white Warbler. A very dark juvenile Peregrine Falcon arrived on 27th, which showed features consistent with west-coast North American populations. Further investigation into this bird is ongoing.
The hysteria calmed down briefly on 27th as the weather was too challenging to do much birding. Just as a reminder, the Corvo birding season does not typically start until early October, yet already a whole season's worth of birds had been recorded before most of the regular visiting birders arrived.
On 28 September the weather improved and birders scrambled across the island to see what vagrants had arrived in the previous few days' inclement conditions. There was a new Yellow-throated Vireo, two Philadelphia and several Red-eyed Vireos, two Black-and-white Warblers, an Ovenbird, three American Redstarts, an American Yellow Warbler, Common Yellowthroat, Wilson's Warbler and the Mourning Warbler all logged – surely one of the best days experienced on Corvo.
Over the following few days there were additional American Yellow Warblers, Common Yellowthroats, an American Cliff Swallow, Philadelphia Vireos, even more Black-and-white Warblers and a few American waders and ducks were found. New species for the year discovered included Merlin, Northern Waterthrush and American Buff-bellied Pipit. There was also a Brown Booby flying around offshore.
The interlude
It was now early October and the bulk of the birders started to arrive just as all the birds began to clear out. The weather was improving and the dreaded Azores High threatened to re-establish over the mid-Atlantic. There were still plenty of good birds around, but new arrivals included just the odd Philadelphia and Red-eyed Vireos on 2nd, Common Yellowthroat and Northern Waterthrush on 3rd and a Baltimore Oriole on 4th (plus a new juvenile Brown Booby). Luckily, more rain and wind on 5th brought in some waders, a new Red-eyed Vireo and an American Yellow Warbler.
Despite strong westerlies on 6 October, no new birds were discovered, and when a Common Cuckoo arrived on 7th – a mega in the Azores and first record for Corvo – things had started to appear from the wrong direction (Europe!). A new American Redstart kept hopes alive and optimism was rekindled on 8th, with new finds including White-eyed Vireo at the Lighthouse Valley and a Scarlet Tanager discovered by the Hungarian team. There were three American Golden Plovers at the reservoir.
Hope died again on 9th, with no new birds apart from that there were now seven American Golden Plovers at the reservoir – a record for Corvo and part of a wider influx across the Azores.
White-eyed Vireo, Tennessee Valley, Corvo. First-calendar-year birds are generally dark-eyed but a pale eye can develop later in the autumn as shown in this presumed first-year bird (Peter Alfrey).
A few new bits on 10th included a Greenland Redpoll in the caldera and new American Redstarts and Ovenbirds, but there were still plenty of long-staying birds around. On 11-12th it was quiet, apart from the arrival of a kestrel found by Magnus Robb that on smart forensic inspection and with the help of Dick Forsman was identified as a Lesser Kestrel, the first for Corvo and second for the Azores.
Magnus Robb also carried out some nocturnal recording on the island and picked up singing band-rumped storm petrel species and a fly-over American Golden Plover. The quiet spell continued to the 13th, but on 14th a new American species was found – a Bobolink. Meanwhile, a Desertas Petrel was seen from the Corvo to Flores ferry. Wet and windy weather on 15th prolonged the quiet spell but the weather had finally broken again, westerly winds had resumed and new birds were being anticipated.
The countdown to 19 October
The rain and strong winds had stopped on 16th and once again birders scrambled across the island in search of new arrivals. Jouni Riihimäki and Ilkka Sahi found a Common Nighthawk, Zbigniew Kajzer found the season's first Rose-breasted Grosbeak, Bjorn Frikke found the year's first Yellow-billed Cuckoo (Pierre also had one), Max Dettori picked up a Baltimore Oriole, Miguel Berkemeier had an Ovenbird and a few guys saw new Red-eyed Vireos.
Meanwhile, on the neighbouring island of Flores, Aristide Parisod and his team had additional Ovenbirds and Red-eyed Vireos. On the 18th they also had Common Yellowthroat, Green Heron and Great Blue Heron.
Tree Swallow, Lighthouse Valley, Corvo. The characteristic first-calendar-year primary moult of this species is shown in this composite image (Vincent Legrand).
More westerlies and rain on 17th hampered birding, but Harry Murphy found a new Yellow-billed Cuckoo and there was a Bobolink found by Ilkkha Vieno. During the continuing challenging weather conditions Alberto Nava found a Tree Swallow at the Lighthouse Valley on 18th and Harry and Pierre discovered a Swainson's Thrush. Little did they know that this was the harbinger of an unprecedented WP arrival of this species …
Thursday 19 October
No fewer than 25 individual American landbird vagrants arrived on this now-historic date – the highest number to arrive in one day since 28 October 2005, when a flock of 26 Chimney Swifts arrived on the island. However, it wasn't Chimney Swifts this time – in fact there was not a single Chimney Swift on Corvo in 2023. The invasion this year was an invasion of Catharus thrushes with between 12 and 15 Swainson's and three Grey-cheeked Thrushes being discovered in one day.
Additionally, there were three or four Rose-breasted Grosbeaks, three Indigo Buntings, a new Ovenbird and a Pale-bellied Brent Goose. Furthermore, there were still many long-staying vagrants present on 'The Rock', including American Cliff Swallow, Tree Swallow, Tennessee Warbler, Scarlet Tanager and Bobolink.
Swainson's Thrush, Lower Road, Corvo. An incredible 17 birds were logged on the island on and in the days after 19 October. Across the Azores archipelago, an amazing 28 birds were logged in total. There had only been 10 previous historical records up to 2020 (Vincent Legrand).
On the neighbouring island of Flores, Aristide and team found another Swainson's Thrush, and over the next few days, an additional 11 Swainson's Thrushes were recorded across the Azores archipelago with an estimated 17 on Corvo – an incredible 28 birds in total.
It was raining so hard on 20th that not many birders got out and most were also booked to leave the island that day – unbeknown to them just before the next period of mayhem started. Unfortunately, the usual peak time for Corvo (early-mid October) did not optimise birding for 2023 – an acute reminder of the perils of predicting vagrancy from long-term trends in a rapidly dynamic and changing climate.
Rupert Hafner found a stunning near-adult Yellow-crowned Night Heron on the rocky shore of the village on the 20th and there was a new female Scarlet Tanager found by Max and a Bobolink by Zbigniew. A new Grey-cheeked Thrush took the island total to four.
Saturday 21 October was the last day for Pierre-André Crochet, who had been on the island for 28 days. Another three Grey-cheeked Thrushes were found, taking the total to seven. Pierre and Harry found a new White-eyed Vireo in Tennessee Valley, there was a flock of three Bobolinks found by Zbigniew and a couple of new Indigo Buntings.
Roosting Common Nighthawk, Corvo (Vincent Legrand).
Late October mayhem
On 22 October, David Monticelli and I arrived at Corvo Airport, taking the baton off the departing Pierre and others, leaving only four birders on the island (David, Harry, Zbigniew and myself). We only had a few hours of the day left when we arrived but in a short drive up to Fojo we witnessed the fall of 19th with Swainson's Thrushes along the road. As part of a long-term vagrant ringing and isotope study, David attempted to net a Swainson's but instead caught a Grey-cheeked Thrush. Within that short time, we also saw Red-eyed Vireo and Indigo Bunting and, at last light, we had the Yellow-crowned Night Heron along the shore in the village. Not a bad start at all.
We said goodbye to Harry on 23rd. We had a Ring-billed Gull and Rose-breasted Grosbeak in the valley, as well as what was now becoming the usual three or four Swainson's Thrushes hopping along the road on the way back. There was also a Scarlet Tanager found in the village.
On 24th, David and I were enjoying collecting more Swainson's and Grey-cheeked Thrushes that had taken up temporary residence of the island roads. However, as we had booked last-minute flights to Corvo, we were now 'homeless' as the famous Comodoro Guesthouse was fully booked. Zbigniew, who was on his way back to Poland, vacated a small house in the village, so we occupied that and luckily avoided living in the campsite toilet block for the week.
The classic scene of late October 2023 on Corvo: a scan ahead on most sections of the lower road would reveal the distinctive shape of a Catharus thrush (Peter Alfrey).
On Flores, meanwhile, the strengthening westerly wind had grounded all flights and Aristide and team got stranded. The cancelled flight proved fortuitous for them with the tally for Flores that day including two Scarlet Tanagers, Common Yellowthroat, Ovenbird, Swainson's Thrush, Solitary Sandpiper and Ring-billed Gull (possibly the same bird seen previously on Corvo).
Putative Common Gallinule, Ribeira da Ponte, Corvo. A potential first for the Western Palearctic. Two apparently newly arrived moorhens were encountered during the unprecedented American vagrant influx, including one found dead on the airfield. A sample from the dead specimen is currently being DNA analysed to confirm an identification. Field characters of Common Gallinule include a larger, more gallinule-like structure, with longer bill and more extensive and squared off forehead shield, rusty tinge to the mantle and scapulars, grey neck and yellow confined to a triangle tip on the bill characteristics all shown in the bird above (Peter Alfrey).
Wednesday 25 October was a special day (see Appendix 4). I thought I'd lucked in by finding a newly arrived moorhen in a hedge at Ribeira da Ponte – a putative Common Gallinule which we had been on the lookout for years on Corvo – but while David and I were looking for it (and trying to catch it, as we knew we would need DNA to confirm its identify), Tobias Epple and his birding tour group found an Eastern Wood Pewee back at the village, so we abandoned the nets and headed over there.
However, it was Flores that stole the show that day as Aristide's team found a Least Bittern and an additional 10 new American landbirds including Cape May Warbler, Northern Waterthrush, Blackpoll Warbler, American Cliff Swallow, three Swainson's and two Grey-cheeked Thrushes, and an Indigo Bunting, all within a 2-km stretch of coast.
Eastern Wood Pewee, Lower Fields, Corvo (Peter Alfrey).
What had just happened?! Given what was on Flores, David and I were somewhat disappointed with our 'dodgy' moorhen (and David hadn't even seen that). We had been birding from dawn to dusk and had very little to show for it in the way of new finds, while other birders were having the best days of their lives.
So, on 26th, unwavering from our mission, we got up at dawn and birded the Lower and Middle Fields. Nothing. So, we now started wavering (in other words, having a meltdown) and decided to try our luck on the reservoir slopes. That proved to be a good decision: a haul of Grey Catbird, Buff-breasted Sandpiper, Philadelphia Vireo and another Swainson's Thrush, plus a Surf Scoter that was bizarrely flying over the fields, soon made us ecstatic! As we bounced our way back to the village we also picked up the White-eyed Vireo that Pierre and Harry had found at Tennessee Valley and, back at the village, David found a Blackpoll Warbler.
The westerly winds were unrelenting. On 27th, David and I headed to Lighthouse Valley, where before 11 am we had found Bay-breasted Warbler and Wood Thrush. Back at the village Tobias and his group had an American Bittern fly in off the sea. In a bizarre twist to the moorhen saga, we noticed a dead bird on the runway which the airport staff retrieved for us. A DNA sample has been sent to Martin Collinson's lab for processing.
From what we could see on the slightly decomposed bird it was a different individual to that observed in the field at Ribeira da Ponte. There are European Common Moorhens on the neighbouring island of Flores and two pairs breed in the caldera on Corvo. However, these apparently newly arrived birds in atypical habitat were surely migrants, arriving in strong westerly winds in the company of lots of other American vagrants. Tobias also discovered an American Coot in the caldera on the same day. It will be fascinating to see what the DNA results reveal.
Grey Catbird; Bay-breasted Warbler; Wood Thrush (David Monticelli).
A quiet finish
The final few days of our nine-day stay on Corvo were quieter, although we estimated that we had seen 11 different Swainson's Thrushes and seemed to find a few new birds including Common Yellowthroat, Black-and-white Warbler, Rose-breasted Grosbeaks, Red-eyed Vireos, Scarlet Tanager and a couple of nominate Common Redpolls (only the second record for the Azores of this subspecies; most redpolls seen on Corvo are Greenland rostrata).
Tobias and his group left on the 27th and Jose Alves arrived, finding a Todd's Canada Goose on the 29th. On 30th we took a flight off Corvo and Jose got the boat back to Flores, turning out the lights on the best-ever Corvo season.
Yellow-crowned Night Heron, Corvo (Peter Alfrey).
Appendices
Appendix 1
Breakdown of all American landbird species seen on Corvo during autumn 2023.
| Species | Individual count |
| Northern Harrier | 1 |
| Merlin | 1 |
| Peregrine Falcon | 1 |
| Common Nighthawk | 1 |
| Yellow-billed Cuckoo | 3 |
| Grey Catbird | 1 |
| Grey-cheeked Thrush | 9 |
| Swainson's Thrush | 17 |
| Wood Thrush | 1 |
| Eastern Wood Pewee | 1 |
| Yellow-throated Vireo | 1 |
| White-eyed Vireo | 2 |
| Philadelphia Vireo | 8 |
| Red-eyed Vireo | 30+ |
| American Buff-bellied Pipit | 4 |
| American Cliff Swallow | 9 |
| Tree Swallow | 1 |
| Mourning Warbler | 1 |
| Common Yellowthroat | 11 |
| Wilson's Warbler | 1 |
| Ovenbird | 11 |
| American Yellow Warbler | 5 |
| Northern Parula | 1 |
| Bay-breasted Warbler | 1 |
| Blackburnian Warbler | 1 |
| Chestnut-sided Warbler | 1 |
| American Redstart | 4 |
| Blackpoll Warbler | 1 |
| Tennessee Warbler | 1 |
| Black-and-white Warbler | 18 |
| Northern Waterthrush | 3 |
| Indigo Bunting | 6 |
| Rose-breasted Grosbeak | 11 |
| Scalet Tanager | 5 |
| Bobolink | 4 |
| Baltimore Oriole | 4 |
Appendix 2
Pressure charts for 18-19 September 2023, showing a fast-moving depression moving from Newfoundland towards the Azores and on to the UK.
Appendix 3
The prelude to the large fall on 19 October with a fast-moving depression moving out of Newfoundland and then sweeping south-east to the Azores.
Appendix 4
The big arrival in late October occurred on the back of a continuous conveyor belt of westerlies on 24 October across the Atlantic and an intensifying low pressure by 25th.
Acknowledgements
Thanks to Pedro Ramalho, secretary of the Portuguese Rarities Committee, for collating and compiling the statistics and to Pierre-André Crochet and Tim Collins for collating the daily logs for Corvo throughout the autumn.
References
Alfrey, P. 2006. Eye of the Storm. Birdwatch 172: 37-40 [available online here].
Alfrey, P. 2018. Nearctic Vagrants on Corvo, Azores, in 2005-2017. Dutch Birding 40 (5) 297-317.
Jones, J. 2023. Review of the Week: 18-24 September 2023. BirdGuides.com [available online here].
